Coordination Polymers of Zn and Cd Based on Two Isomeric Azine Ligands: Synthesis, Crystal Structures, and Luminescence Properties

Abstract

Metal-organic 1D coordination polymers of Zn(II) and Cd(II), [{Zn(3-Bphz)(H₂O)₄}(3-Bphz)(NO₃)₂]_n (I), [Zn(3-Bphz)I₂]_n (II), [Cd(3-Bphz)I₂]_n (III), [Cd(4-Bphz)(CH₃COO)₂(H₂O)]_n (IV), and [Cd(4-Bphz)(NO₃)₂(H₂O)₂]_n (V), containing azines of the N,N' type, 1,2-bis(pyridin-3-ylmethylene)hydrazine (3-Bphz) and 1,2-bis(pyridin-4-ylmethylene)hydrazine (4-Bphz), as bridging ligands are synthesized. The compositions and structures of the compounds are confirmed by the data of elemental analysis, IR and NMR spectroscopy, and single-crystal X-ray diffraction analysis (CIF files CCDC nos. 1812634–1812638 for I–V). Coordination polymers I–III have zigzag structures. The octahedral environment of the Zn²⁺ ion in compound I is formed by two 3-Bphz ligands and four water molecules. The external sphere contains nitrate anions and uncoordinated 3-Bphz molecules. In isomorphous compounds II and III, the tetrahedral environment of the metal is formed by two nitrogen atoms of two bridging 3-Bphz ligands and two iodine atoms. Coordination polymers IV and V are linear. The coordination polyhedron of the Cd²⁺ ion in compound IV is a pentagonal bipyramid, two vertices of which are occupied by the nitrogen atoms of two 4-Bphz molecules, and the equatorial plane is formed by two bidentate-chelating acetate anions and one water molecule. In compound V, the octahedral environment of the Сd²⁺ ion is formed by two molecules of the 4-Bphz ligand, two monodentate nitrate anions, and two water molecules. All complexes are weak luminophores emitting in the blue-green spectral range.